Biological complexity: removing Dad's mitochondria (Introduction)

by David Turell , Thursday, March 23, 2017, 19:22 (2802 days ago) @ David Turell

Male mitochondria must be destroyed in sperm to maintain the inheritance of maternal mitochondria as the rule. This is the first example found:

http://www.the-scientist.com/?articles.view/articleNo/48891/title/Enzyme-Required-for-M...

"Most animals inherit mitochondria from their mothers. Now, at team of scientists has shown that, in Drosophila, the paternal contribution of mitochondrial DNA (mtDNA) is degraded in the sperm in a process that depends on a subunit of the fruit fly mitochondrial DNA polymerase called Tamas.

“'What’s striking about this study is that this gene, tamas, encodes a subunit of the mitochondrial DNA polymerase, which is the enzyme responsible for replicating the mtDNA,” said Damian Dowling of Monash University in Melbourne, Australia, who did not participate in the work. “It’s a completely new function for this gene that was not known prior to this study."

"The role for Tamas is “surprising,” said Eli Arama of the Weizmann Institute of Science in Rehovot, Israel, who was not involved in the study. “Instead of replicating the DNA, basically it is required to degrade it,” he explained.

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"The researchers hypothesized that the capability of the Tamas enzyme to degrade nucleotides would be responsible for the destruction of paternal mtDNA, but they showed that a Tamas protein without exonuclease activity still resulted in sperm without mtDNA. They also found that the replication function of Tamas did not appear to play a role in eliminating paternal mtDNA.

“'It seems that the catalytic activity of this subunit of mitochondrial DNA polymerase is not required for the degradation of the mitochondrial DNA, which leaves us with a lot of questions about the mechanism,” said Arama. “It’s not the canonical polymerase or exonuclease [functions], but probably another function that this protein has, which remains to be discovered.” Arama noted that Tamas may act in a complex with other proteins to facilitate the elimination of paternal mtDNA.

“'More evidence is required to make sure that Tamas is directly involved in the degradation,” Hansong Ma of the Gurdon Institute at the University of Cambridge in the U.K., who was not involved in the study, wrote in an email to The Scientist.

"According to coauthor Patrick O’Farrell of UCSF, another open question is how general the role for a mitochondrial DNA polymerase in elimination of paternal mtDNA is. “Maternal inheritance is really widespread,” he said. “There are a few exceptions, but for the most part it’s found throughout the entirety of phylogeny, and we don’t know whether exactly the same mechanisms are used.”

“'Typically when we find these sorts of outcomes in fruit flies, they’re broadly applicable across animals,” Dowling told The Scientist. “I wouldn’t be surprised at all if this extends to our own species.”

"Ma also noted that mtDNA destruction may take place outside of sperm. “This paper provides good evidence that Tamas is required for the elimination of mtDNA during spermatogenesis,” she wrote, “but we don’t know whether this role of Tamas is specific to testis, where mtDNA is purposefully eliminated to ensure maternal inheritance of mtDNA, or [if the enzyme performs this function] in other tissues.'”

Comment: Such a removal mechanism must be present and it will be fully discovered as research continues. We still don't know why mitochondria must be maternal. That is one of he mysteries.